Field of Invention
Various embodiments of the present invention relate to an optical communication system, and more particularly, to a feedback amplifier that is capable of sensing an input signal, and controlling a gain of an amplifier.
Description of Related Art
Optical access networks are evolving into optical multiple access networks that use the PON (Passive Optical Network) technology. In such a passive optical network, bust mode optical signals are used. When a bust mode optical signal converts from a packet of a channel to a packet of another channel, the voltage of the optical signal suddenly changes significantly.
An optical receiver of an optical communication system needs both a wide dynamic range and high receiving sensitivity. In such an optical receiver, a preamplifier is positioned at a first terminal where a signal is input, and the performance of the preamplifier depends on the performance of a feedback amplifier that is used as the preamplifier.
Such a feedback amplifier has an amplifier circuit for sensing a bust packet input signal and for amplifying the same. The feedback amplifier provides a feedback circuit for sensing a peak value of the bust packet input signal and for controlling the level of the output voltage of the sensed signal. Herein, the feedback circuit includes a feedback resistance connected between an input terminal and output terminal, and a feedback transistor in parallel to the feedback resistance. Herein, the feedback transistor may control the current flowing through the feedback circuit and the output voltage as a control signal is applied to its base.
Such a feedback amplifier senses a bust packet input signal by the voltage level, but it cannot sense a bust packet input signal when the voltage level of the bust packet input signal is extremely low, which is a problem.
Furthermore, for applying a control signal to the base of the feedback transistor, there is a method of configuring a separate gain control signal generating circuit outside the feedback amplifier to generate a control signal, and a method of positioning a bias circuit inside the feedback amplifier to generate a control signal in itself. However, since the control signal changes in response to the input signal, if there is a big difference in the input signal, it is not possible to freely control the gain of the preamplifier, which is a problem.